Modern digital networks are made to operate in a multimedia environment for transporting different types of data (pure data or digitized information signals including voice, image, video, etc) over the same network, while ensuring the compliance with the requirements specific to each kind of traffic.
For instance, one may notice that the information provided by various users can be divided into different types. These include real-time information (such as voice information) that must be transmitted to the end-user within predefined limited time-delay restrictions, and non-real-time information. If some real-time information is not transferred within said time delay, it should simply be discarded.
In this case, recovery of the original signal, at an end-user location is made possible to some extent, by providing interpolation/extrapolation techniques, in a data packet transmission environment. These techniques do provide solutions to overcome the "loss" of only a limited number of discarded consecutive packets. They do not overcome the delay restriction requirement.
On one hand the information may be considered as including : a so-called Reserved traffic information whose transmission must be guaranteed with predefined maximum delay according to conditions contractually agreed upon by both parties, i.e. end-user and network owner ; and a Non-Reserved (NR) information, such as certain control information or traffic of specific sources to be vehiculated over the network with no specific time constraint, but which traffic should be optimized for network efficiency.
On the other hand, one should recall that different techniques have been developed, such as packet switching techniques, whereby the digitized data are arranged into so called bit packets as already mentioned, and circuit switching techniques.
The basic advantage of packet switching techniques as compared to circuit switching techniques, is to allow a statistical multiplexing of the different types of data over a line which optimizes the transmission bandwith. The drawback of packet switching techniques compared to circuit switching techniques, is that it introduces jitter and delay, which, as already considered, may be detrimental for the transmission of isochronous data, like video or voice. This is why methods have been proposed to control the network in such a way that delay and jitter are bounded for every new connection that is set-up across a packet switched network.
These methods have been described, for instance a co-pending European Application 94480097.8. All these methods include, for any end user requesting service or any control data to be transported over the network, establishing a path through network high speed links (or lines) and nodes or ports, with optimal use of the available transmission bandwidth.
Basically, one may allocate predefined bandwidth to Reserved traffic (including real-time) on the basis of contractually defined parameters, and then allocate whatever is left of the bandwidth to Non-Reserved traffic on a fixed basis.
But, bearing in mind that instantaneous traffic is eminently variable for both Reserved and Non-Reserved traffic, any fixed bandwidth assignment is naturally inefficient as far as the efficiency of global network utilization is concerned.
A first improvement consists in precomputed oversized bandwidth allocation on a source by source basis, with the provision of means for detecting instantaneous congestion occurring within the network and for monitoring some sort of "slowing-down" mechanism. Such a mechanism has already been described in the above mentioned copending European Application as well as in U.S. Pat. No. 5,280,470. In the mentioned co-pending application, the slowing-down mechanism is only used to control congestion at the node switching level through management of a switch back-pressure signal. In the U.S. Pat. No. 5,280,470 slowing-down is operated over reserved bandwidths only when congestion is detected in network nodes and no increase is allowed, which may result in low link utilization in case of some sources being non-active. Accordingly, the data sources are not really taken into account on a dynamic basis. In other words, the considered prior art system does not provide true dynamic sharing among connections but only helps resolving traffic congestions temporarily by sending a slow-down message back to sources.